2,点电荷系的电场中 (与路径无关) Ab=o(E1+E2+.+En)l jga+jg.ea+jgEm 4+++4 460 Tia Tib２．点电荷系的电场中 =  + + + • b a a b n A q ( E E E ) dl      0 1 2    = • + • + • b a b a b a q E dl q E dl q E dl        0 1 0 0 = + + + =  − i i a i b i n ) r r ( q q A A A 1 1 4 0 0 1 2   (与路径无关)